The long-term objective of this study is to explain the mechanism of insulin action in the human body in order to contribute towards improvement of clinical treatment of diabetes. The specific aim of the proposed study is to elucidate the mechanism by which the interaction of insulin with its cellular receptor leads to the stimulation of phosphodiesterase. This year, we plan to purify this enzyme from fat cells. The methods of purification will include gel-filtation, ion-exchange chromatography, and electrophoresis. The biochemical properties of phosphodiesterase in its basal, insulin-stimulated and catecholamine-stimulated forms will be carefully examined. The study may provide some clue on the possible mechanism of insulin action.